Technical Field
The present disclosure relates to an electrophotographic photoconductor, and an image forming apparatus and a process cartridge.
Description of the Related Art
In an image forming method performed by an image forming apparatus, an image is formed by exposing an electrophotographic photoconductor (hereinafter may be referred to as “photoconductor”) to the processes of charging, irradiation, developing, transfer, etc. Nowadays, organic photoconductors (OPC) that use organic materials are widely used as the electrophotographic photoconductor in terms of their flexibility, thermal stability, and film formation property.
The photoconductor is required to have much higher durability and stability in accordance with the rapid progress of image forming apparatus technologies in terms of colorization, speeding up, and higher definition. An abrasion resistance of the photoconductor was improved drastically by improving a surface layer such as a protective layer. In contrast, an electrical durability and a chemical durability comes to be demanded to each layer constituting the photoconductor such as a photosensitive layer, an intermediate layer and an undercoat layer.
Through repeated exposure to the charging and neutralization processes in electrophotography, the organic materials contained in the photoconductor will gradually denature. As a result, charge trapping or charge property change will occur in the layers. In this way, an electric characteristic of the photoconductor deteriorates and an electrical stability in the long usage cannot be maintained. Deterioration in charge property largely affects the quality of the output images. For example, decrease in image density, background fog, residual image, and/or non-homogeneous image after continuous printing may be caused. Possible reasons of these problems are a characteristic of the undercoat layer of the photoconductor. Future improvement of the undercoat layer is necessary for a durability and a high stabilization of the photoconductor.
Generally, the undercoat layer is provided for the purpose of following three functions:
a function of leak resistance by covering surface of the support (hereinafter “leak resistant function”), a function of preventing charge injection from the support into the photosensitive layer (hereinafter “charge injection prevention function”) and a function of transporting charges generated in the photosensitive layer to the support (hereinafter “charge transport function”). Improving these functions are demanded.
The undercoat layer comprising the titanium oxide particle is proposed. However, leak resistant function by covering surface of the support is insufficient because a thickness of the undercoat layer is range of 1 μm to several μm. The content of the titanium oxide particle is approximately 80% of the undercoat layer, it is difficult to maintain the dispersibility of the titanium oxide particle in the undercoat layer because there is much content of the titanium oxide particle. So, the leak point caused by fine cracks of the undercoat layer occurs. As a result, the abnormal image by the background fog occurs after a long period of use. In addition, a secondary undercoat layer overlying the undercoat layer is proposed in order to provide leak resistant function. However, the photoconductor function cannot be maintained enough because electric charge accumulations increase with the increase of the layer interface. Furthermore, the undercoat layer comprising tin oxide particles or zinc oxide particles is proposed. Thickness of the undercoat layer is several 10 μm, and the undercoat layer can make into a thick film while controlling volume resistance. However, it is difficult for the undercoat layer to satisfy all requesting properties such as, improving of leak resistant function by thickening the undercoat layer, and electric characteristic stabilization.